Method of making a face commutator

ABSTRACT

A face commutator for a dynamo electric machine comprising a moulded synthetic resin body arranged to be secured to a dynamo electric machine rotor shaft for rotation therewith and a plurality of conductive segments carried by the body. The segments are disposed on the body in a circle having its centre on the rotational axis of the body, and each segment extends radially with respect to the axis of rotation. The front faces of the segments are generally co-planar and their rear faces are presented to the body, each segment being keyed into the moulded body at both its radially innermost and its radially outermost end of its rear face. Each segment is keyed to the body at its radially outermost end of its rear face by means of a pair of rearwardly extending, divergent integral projections. The specification also discloses and claims a method of manufacturing the face commutator.

'United States Patent 1 Bowcott Dec. 16, 1975 METHOD OF MAKING A FACE [73] Assignee: The Lucas Electrical Company Limited, Birmingham, England [22] Filed: Jan. 8, 1975 [21] Appl. No.: 539,340

[30] Foreign Application Priority Data Primary Examiner-Carl E. Hall Attorney, Agent, or Firm-Olson, Trexler, Wolters, Bushnell & Fosse, Ltd.

[ 5 7] ABSTRACT A face commutator for a dynamo electric machine comprising a moulded synthetic resin body arranged to be secured to a dynamo electric machine rotor shaft for rotation therewith and a plurality of conductive segments carried by the body. The segments are disposed on the body in a circle having its centre on the rotational axis of the body, and each segment extends radially with respect to the axis of rotation. The front faces of the segments are generally co-planar and their rear faces are presented to the body, each segment being keyed into the moulded body at both its radially innermost and its radially outermost end of its rear face. Each segment is keyed to the body at its radially outermost end of its rear face by means of a pair of rearwardly extending, divergent integral projections. The specification also discloses and claims a method of manufacturing the face commutator.

2 Claims, 11 Drawing Figures III] US. Patent Dec. 16, 1975 METHOD OF MAKING A FACE COMMUTATOR This invention relates to a face commutator for a dynamo electric machine.

A face commutator according to theinvention includes a moulded synthetic resin body arranged to be secured to a dynamo electric machine rotor shaft for rotation therewith, the body carrying a plurality of conductive segments disposed on the body ina'circle having its centre on the rotational axis of the body, said segments extending radially with respect to said axis with front faces thereof generally coplanar and their rear faces presented to the body, each segment being keyed into the moulded body at both the radially inner and radially outer ends of its rear face and each segment being keyed to the body at the'radially outer end of its rear face by means of a pair of rearwardly extending, divergent, integral projections.

Preferably the rear face of each segment is formed with a channel, one wall of which is defined by said pair of projections and the other wall of which is defined by a rearwardly extending lug at the radially inner end of the segment the face of said lug presented to said projections being under-cutand so providing keying between the segments and the body at its radially inner end.

The invention further resides in a method of manufacturing a commutator as specified above, the method comprising starting with an annular blank of conductive material, forming in one face of the blank an annular channel so as to define upstanding circumferential flanges at the inner and outer peripheries of said one face of the blank, forming in said one face of the blank a plurality of equi-angularly spaced radially extending grooves, said grooves extending over the whole radial width of the blank and being deeper than the thickness of the blank so as to produce upstanding ribs on the opposite face of the blank, said grooves dividing the blank into a plurality of interconnected segments, performing a stamping operation on the outer peripheral flange portion of each segment to bifurcate the flange portion and deform the two limbs so produced away from one another to define a pair of divergent projections at the radially outer end of each segment, moulding a synthetic resin body onto said one face of the blank, providing means on each segment whereby an electrical connection can be made thereto, and then removing said ribs from the other face of the blank to separate the segments.

Preferably the operation performed to produce said radial grooves is a stamping operation and has the effect of deforming the inner peripheral flange portion of each segment such that its radially outer face is undercut.

One example of the invention is illustrated in the accompanying drawings wherein:

FIGS. 1, 3, 5 and 7 are plan views respectively of a face commutator at various stages in its manufacture,

FIGS. 2, 4, 6 and 8 are sectional views on the appropriately marked lines in FIGS. 1, 3, 5 and 7 respectively,

FIG. 9 is a fragmentary side elevational view of the component shown in FIG. 8, but to an enlarged scale,

FIG. 10 is a simplified sectional view of the commutator, and FIG. 11 is an enlarged view similar to FIG. 9 showing part of the commutator body in section.

Referring to the drawings, the face commutator includes a moulded synthetic resin body '11 (FIG. 10) carrying a plurality of copper segments 12 on one face thereof. The body has therein a bore 13 containing a liner 13a whereby the commutator can be mounted on the rotor shaft of a dynamo electric machine for rotation with the shaft, and the segments 12 are disposed in a circle about the axis of the bore 13. The segments 12 are generally equi-angularly spaced, and are insulated from one another byprojecting portions 11a of the body 11. The surfaces of the segments 12 remote from the body are generally co-planar, and constitute the brush engaging surface of the commutator.

The commutator is manufactured in the following manner. I

An annular copper blank 15 is stamped from a sheet of copper, and is subjected on one face thereof to a stamping operation to produce in said one face an annular channel 16. The side walls of the channel 16 define outer and inner parallel, peripheral flanges 17, 18. Said one face is then subject to a second stamping operation using a tool of V-shaped cross-section to produce in said one face a plurality of equi-angularly spaced radially extending grooves 19 of V-shaped cross-section. The tool used to form the grooves is sufficiently wide that the grooves extend over the whole radial width of the blank. A further stamping tool also of V-shaped cross-section, but of smaller apical angle than the preceding tool is used to extend the depth of the grooves 19 such that the grooves 19 are deeper than the thickness of the blank 15, and corresponding ribs 21 are produced on the opposite face of the blank. It will be appreciated that if a suitable tool is available then the two stages in the formation of the grooves 19 can be performed in a single operation. The formation of the grooves 19 and ribs 21 divides the blank 15 into a plurality of segments 12 each connected to its neighbour by the material of the appropriate rib 21. Additionally, the stamping operation to produce the grooves 19 deforms the inner peripheral flange 18 such that its inner surface 22 is undercut. This can be best seen in FIG. 6, where the inclination of the surface 22 has been exaggerated.

The blank 15, after the formation of the grooves 19 and ribs 21, is then indexed through half the angle subtended by adjacent grooves 19 and a further stamping operation is performed on each segment 12. The further stamping operation bifurcates the portion of the flange 17 of each segment to define a-pair of projections 17a. The stamping operation further serves to deform the projections 17a away from one another so that each segment includes at its outer periphery a pair of integral, and divergent projections 17a. FIG. 9 shows the divergent projections 17a, and additionally in dotted lines shows the form of the portions of the flange 17 .of each segment prior to the bifurcating operation.

The blank is next mounted in a mould, and synthetic resin is injected into the mould to form the commutator body 11. Said one face of the blank is presented to the synthetic resin, and the molten synthetic resin flows into the channel 16, and the grooves 19. Owing to the divergent nature of the projections 17a of each segment then the grooves 19 adjacent the outer periphery of the blank are of a re-entrant nature. Thus when the synthetic resin material sets each segment 12 is keyed, at its outer periphery, to the body 11 by the divergent projections 17a. Similarly, the molten synthetic resin material flows under the undercut surface 22 adjacent the inner periphery of each segment, and when the synthetic resin material sets each segment is keyed to the body 11 adjacent its inner periphery. The blank together with its body are then milled to produce in each segment a radially extending slot for receiving connecting wires. When the body is moulded, the axial bore thereof is provided with a liner for receiving the rotor shaft of the dynamo electric machine utilizing the commutator. The body of the commutator extends between the liner and the inner peripheries of the segments to ensure that the segments are not electrically interconnected by the liner. After formation of the slots the body is mounted on the rotor shaft and the electrical connector between the segments and the armature of the rotor assembly are made. Finally, the face of the commutator remote from the body 11 is machined to remove the rib 21 thereby physically and electrically separating the segments from one another. Additionally, the machining operation renders the brush receiving faces of the segments coplanar and at right angles to the rotor shaft axis. Each segment is of course individually strongly keyed to the body 1 1 at its outer periphery by the divergent projections 17a, and adjacent its inner periphery by the under cut surface 22.

I claim:

1. A method of manufacturing a face commutator, comprising starting with an annular blank of conductive material, forming in one face of the blank an annular channel so as to define upstanding circumferential flanges at the inner and outer peripheries of said one face of the blank, forming in said one face of the blank a plurality of equi-angularly spaced radially extending grooves, said grooves extending over the whole radial width of the blank and being deeper than the thickness of the blank so as to produce upstanding ribs on the opposite face of the blank, said grooves dividing the blank into a plurality of interconnected segments, performing a stamping operation on the outer peripheral flange portion of each segment to bifurcate the flange portion and deform the two limbs so produced away from one another to define a pair of circumferentially divergent projections at the radially outer end of each segment, moulding a synthetic resin body onto said one face of the blank, providing means on each segment whereby an electrical connection can be made thereto, and then removing said ribs from the other face of the blank to separate the segments.

2. A method as claimed in claim 1 wherein the operation performed to produce said radial grooves is a stamping operation and has the effect of deforming the inner peripheral flange portion of each segment such that its radially outer face is undercut. 

1. A method of manufacturing a face commutator, comprising starting with an annular blank of conductive material, forming in one face of the blank an annular channel so as to define upstanding circumferential flanges at the inner and outer peripheries of said one face of the blank, forming in said one face of the blank a plurality of equi-angularly spaced radially extending grooves, said grooves extending over the whole radial width of the blank and being deeper than the thickness of the blank so as to produce upstanding ribs on the opposite face of the blank, said grooves dividing the blank into a plurality of interconnected segments, performing a stamping operation on the outer peripheral flange portion of each segment to bifurcate the flange portion and deform the two limbs so produced away from one another to define a pair of divergent projections at the radially outer end of each segment, moulding a synthetic resin body onto said one face of the blank, providing means on each segment whereby an electrical connection can be made thereto, and then removing said ribs from the other face of the blank to separate the segments.
 2. A method as claimed in claim 1 wherein the operation performed to produce said radial grooves is a stamping operation and has the effect of deforming the inner peripheral flange portion of each segment such that its radially outer face is undercut. 